1. Field of the Invention
The invention relates generally to audio amplification systems, and more particularly to systems and methods for converting multiple data streams at an input sample rate to one or more output sample rates using dual rate estimate counters.
2. Related Art
Pulse Width Modulation (PWM) or Class D signal amplification technology has existed for a number of years. PWM technology has become more popular with the proliferation of Switched Mode Power Supplies (SMPS). Since this technology emerged, there has been an increased interest in applying PWM techniques in signal amplification applications as a result of the significant efficiency improvement that can be realized through the use of Class D power output topology instead of the legacy (linear Class AB) power output topology.
Early attempts to develop signal amplification applications utilized the same approach to amplification that was being used in the early SMPS. More particularly, these attempts utilized analog modulation schemes that resulted in very low performance applications. These applications were very complex and costly to implement. Consequently, these solutions were not widely accepted. Prior art analog implementations of Class D technology have therefore been unable to displace legacy Class AB amplifiers in mainstream amplifier applications.
Recently, digital PWM modulation schemes have surfaced. These schemes use Sigma-Delta modulation techniques to generate the PWM signals used in the newer digital Class D implementations. These digital PWM schemes, however, did little to offset the major barriers to integration of PWM modulators into the total amplifier solution. Class D technology has therefore continued to be unable to displace legacy Class AB amplifiers in mainstream applications.
One of the problems with conventional digital audio amplifiers relates to the fact that there are many different sources of audio data that may need to be amplified. For instance, the audio data sources may be CD players, MP3 players, digital audio tape players, or other types of data sources. The problem is that these devices may provide digital audio data at different sample rates. A CD player, for example, may output digital audio data at a sample rate of 44.1 kHz, while a digital audio tape player may output data at a sample rate of 32 kHz.
Conventional digital audio amplifiers do not have a particularly efficient mechanism for dealing with the different sample rates that may be encountered. For instance, a conventional system typically has to provide two entirely separate sample rate converters in order to handle two different data sources that have different sample rates. Further, each of these sample rate converters has to be configured to handle a particular predetermined sample rate. If the audio data that is received does not have the predetermined sample rate, the sample rate converter cannot properly convert the input audio data to the sample rate that is used within the processing system of the amplifier. These mechanisms for handling different input sample rates are therefore relatively costly and inflexible.